MYC, a potent proto-oncogene, is aberrantly and widely expressed in human cancers, including the leukemias and lymphomas. The long-term goal of this proposal is to discover molecules that are necessary to sustain MYC-driven tumors, T-cell acute lymphoblastic leukemia (T-ALL) in particular and hence might serve as useful targets for the development of novel molecular therapeutics. Using a transgenic zebrafish model in which murine Myc is expressed in thymocytes and reliably generates T-cell leukemia, I plan to conduct a dominant genetic modifier screen to identify and study "oncorequisite" genes whose mutation delays the onset of leukemia (Aims 1 and 2) and then to clarify the importance of the human orthologs of these genes in T-ALL and neuroblastoma pathophysiology, including the consequences of their inhibition (Aim 3). The rationale and feasibility of this approach are well-illustrated by my recent preliminary data pinpointing a specific gene, encoding dihydrolipoamide S-succinyltransferase (DLST), whose heterozygous inactivation significantly delayed the onset of lymphoma/leukemia in zebrafish expressing the MYC oncogene. Small molecule inhibition of the cc- ketoglutatate dehydrogenase complex (DLST is an pound2 component) by a-keto-p-methyl-n valeric acid (KMV) promoted the rapid regression of zebrafish lymphoma/leukemia, and significantly decreased the viability of humanT-ALL cell lines. Hence, I consider the human ortholog of this Kreb's cycle transferase a promising candidate "oncorequisite" protein for further characterization and testing with available inhibitors in human malignancies. The use of unbiased forward genetic strategies in the zebrafish will circumvent the need for a priori knowledge of contributing genes and pathways in MYC-induced cancer -an innovation that sets this application apart from others in the field - so that any suppressor mutant I identify will automatically qualify as a potentially useful target for inhibition with small molecules or monoclonal antibodies. RELEVANCE: Many human cancers rely on expression of the MYC oncogene for their support. By identifying mutant genes that delay the onset of Myc-driven T-cell leukemia in fish, this project seeks to discover molecules that could serve as useful targets for therapeutic intervention in human cancers.